1. Field of the Invention
The present invention relates to a semiconductor laser with an index waveguide structure and a semiconductor laser module including the semiconductor laser.
2. Description of the Related Art
A conventional semiconductor laser oscillates laser light by taking the light to make a roundtrip inside an optical resonator while amplifying the light by confining the light inside an active layer with an index waveguide structure. The laser light output from the semiconductor laser propagates through the space with a predetermined spread angle. Therefore, the output light usually is provided for use after being collimated and optically-coupled to a coupling target, such as an optical fiber and a recording surface of an optical disk, by a lens system.
In order to increase a saturated optical power of the semiconductor laser, it is effective to increase the width of a waveguide to reduce the electrical resistance. However, excessive expansion of the width of the waveguide is not preferable because a lateral mode of a waveguide mode turns into a multimode. For instance, in Japanese Patent Application Laid-Open No. 2002-280668, the width of the waveguide is increased only at an output facet side while the width of the waveguide at a rear facet side is kept to a width with which a single mode can be achieved, thereby providing a high-intensity laser light in a single mode.
In Japanese Patent Application Laid-Open No. 2002-280668, portions having different waveguide widths are connected by a tapered portion having a continuously changing width. In this description, a waveguide with a structure having such tapered portion being formed will be referred to as a tapered waveguide. On the other hand, a waveguide with a structure having its width being uniform along an optical waveguide direction will be referred to as a straight waveguide.